Nickel plated propeller blade



Nov. 8, 1960 J. w. MEIER 2,

NICKEL PLATED PROPELLER BLADE Filed Oct. 1. 1957 F/G. Z.

v IN VEN TOR. (/O/V/V W ME/ER ATTORNEYS United States Patent NICKEL PLATED PROPELLER BLADE John W. Meier, Suifield, Cnn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Oct. 1, 1957, Ser. No. 687,538

Claims. (Cl. 170-159) This invention relates to an improved aluminum or aluminum alloy aeronautical propeller blade and to the process of plating the blade with a hard wear resistant metal.

While aluminum and aluminum alloy aeronautical propeller blades may be characterized as strong and durable and of lightweight construction, they are not entirely satisfactory in their present state. Due to the relatively soft nature of aluminum and aluminum alloys suitable for propeller construction, they are susceptible to erosion and abrasion damage from water, sand and other air-.

borne particles. Although it has been known to protectively plate such aeronautical propeller blades with hard wear resistant metals such as nickel, in order to overcome these disadvantages, blades so plated have not been completely satisfactory.

Heretofore, aluminum and aluminum alloy aeronautical propeller blades have been nickel plated in accordance with a process whereby succeeding layers of resilient organic materials are affixed to the aluminum or aluminum alloy base blade and serve to prevent crack propagation from the final layer of nickel to the base blade. It has been known practice to coat or impregnate the outermost organic layer with an electro-conductive substance which serves as the cathode in a conventional electrolytic bath wherein the nickel is deposited thereupon to the desired thickness.

Certain disadvantages are known to be associated with this type of plating technique and with propeller blades plated in accordance therewith. The relatively thin layer of electroconductive substance, which is relied upon as a cathode in the nickel plating bath, does not render efiicient service. Deposition of the nickel normally commences at the point where electrical contact is made with the electro-conductive surface and slowly grows outwardly therefrom. As a consequence of this relatively slow deposition of nickel upon the electro-conductive surface, absorption of the electrolyte into the organic materials may be permitted and corrosion of the aluminum or aluminum alloy base blade may result.

Furthermore, the delay in deposition of the nickel over the entire blade surface normally results in contamination of the plating bath by components of the organic materials. Since this contamination is in turn passed on to the deposited hard metal and results in undesirable impurities therein, it is in most cases necessary that the plating be accomplished in two or more stages with new plating baths being utilized for each stage.

Finally, the nickel plated blade, comprising an outer and an inner electrically conductive material separated by a dielectric layer of organic material exhibits the characteristics of an electrical condenser, a highly undesirable feature when the eventuality of lightning striking the blade is considered.

It is the general object of the invention to provide an improved method of hard plating an aluminum or alumi num alloy propeller blade wherein the plate can be applied more rapidlythan has heretofore been the case and without causing any damage to the aluminum body and without dissipating the purity or high quality of the plating material so that the finished propeller blade is more wear resistant and has a longer life than generally similar blades,

It is a more specific object of the invention to provide in a hard plated aluminum propeller blade a resilient material between the blade body and its plate which serves to expedite the plating process during blade fabrication and which serves in the finished blade as a shock cushion between the plate and the body and one which will not create a condenser in the blade construction as has heretofore been found to be highly undesirable.

The drawing shows a preferred embodiment of the invention and such embodiment will be described, but it will be understood that various changes may be made from the construction disclosed, and that the drawing and description are not to be construed as defining or limitlng the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

Fig. 1 is a plan view of an exemplary propeller blade incorporating the features of the present invention and which is nickel plated in accordance with the present invention; and

Fig. 2 is an enlarged scalefragmentary sectional view showing the laminations of the nickel plate, the organic materials and an undercoating of zinc plate on the body of the blade.

Generally speaking, it may be said that the propeller blade 10 of this invention is produced in accordance with a process which includes a plurality of steps wherein succeeding layers of zincate 12, Zinc plate 14, organic materials 16, 18 and 20, all of which are electroconductive throughout their thickness, and a final layer of nickel 22 are affixed to the surface of an aluminum or aluminum alloy aeronautical propeller blade 10.

As used in the following description, the terms aluminum blade, blade and base blade are meant to include a conventional aluminum or aluminum alloy propeller blade whether the blade surface is untreated, has an oxide surface as a result of natural formation or an anodizing process, or has a protective plating of corrosion-resistant metal, such as zinc. The latter two alternatives of blade condition are preferred over the first since the galvanic corrosion protection provided thereby is thought to be highly desirable, Of these two, the corrosion protection provided by Zinc plating is found to be most effective and, accordingly, this construction as illustrated in the drawing which forms a part of this application comprises the preferred embodiment of the invention and will be described hereinafter. v

A first coating of zinc 12 may be provided by first immersing the aluminum base blade 10 in a strong alkaline-type bath containing zinc ions, a method of chemically depositing zinc commonly referred to as a zincating process. A further layer of zinc 14 is then electrolytically deposited on the zinc immersion coating 12 in an acid-type electrolytic bath. It has been found desirable to immerse the blade after zincating in the electrolytic zinc plating bath with the electric current on in order to reduce chemical action of the zinc plating solution with the zincate film 12.

Before any conductive organic material is applied to the zinc plated surface 14 or to the blade surface 10, as the case may be, the surface is thoroughly cleaned in accordance with accepted practices to insure that all foreign or undesirable materials are removed.

The first organic material applied, in a layer 16, is an electro-conductive synthetic rubber resin adhesive, preferably including as its principal constituents a selected mixture of a buna-N type synthetic rubber such as acrylonitrile, a phenolic resin and carbon black dispersed uniform- 1y throughout the mixture. The synthetic rubber while it imparts resiliency to the mixture is not characterized by good, strength characteristics. The phenolic resin, on the other hand, while it does exhibit relatively good strength characteristics, has rather poor ductility qualities. By combining the two constituents in-an appropriate mixture, a desirable compromise of strength and ductility is obtained whereby the resultant material is sufiiciently resilient to inhibit crack propagation therethrough and yet does. not allow shifting of succeeding layers of mater'ial'. The carbon black, which is dispersed in fine particles uniformly throughout the mixture serves, as would be expected, to impart the characteristics of an electrical conductor thereto. The mixture has the property of adhering firmly to zinc as well as to the resin modified neoprene cement, which constitutes the next applied layer 18.

The said adhesive mixture which is used in the layer 16 is thinned with methylethylketone to a suitable consistency for spraying and is then sprayed upon the blade to a thickness of .0001 to .0005 of an inch. It is preferred practice to apply the electroconductive synthetic rubber resin adhesive in two coats to insure uniform and complete coverage of the blade. Ten to fifteen minutes air drying time is customarily allowed after application of each coat to permit evaporation of the solvents therefrom.

The above described layer 16 may be appropriately referred to as a primer coat, its primary function being to insure optimum adhesion to the zinc surface 14. It is to be understood at this point that while the particular conductive synthetic rubber resin adhesive utilized is chosen for reasons of its excellent adhesion to zinc, its adhesion characteristics with respect to untreated and oxide surfaced aluminum are also quite satisfactory. Furthermore, it is considered to be within the scope of the inventive concept to utilize for this purpose other organic adhesives which may be considered to have superior adhesion characteristics with respect to such aluminum surfaces.

The second organic material, applied in a layer 18, is a conductive resin modified neoprene cement. Its principal constituents are preferably neoprene synthetic rubber, phenolic resin and carbon black, dispersed uniformly throughout the mixture. The phenolic resin included in the cement serves to render the mixture compatible with the conductive synthetic rubber resin adhesive, which comprises the preceding layer 16. As a result, excellent adhesion therebetween is obtained and the conductive neoprene rubber cement which comprises the next succeeding layer 20 is also firmly bonded by virtue of its compatibility with the neoprene synthetic rubber which comprises the second principal constituent of the adhesive layer 18. Here, once again, the intermingled carbon black serves to provide electrical conductivity.

The adhesive mixture which is used in the layer 18 is thinned with methylethylketone to obtain a consistency suitable for spray application. Two coats are then applied with an airdrying time of from ten to fifteen minutes following each. It is believed preferable that the minimum thickness of this layer 18 be approximately .0002 of an inch and the maximum thickness be approximately .001 of an inch.

The final layer of organic material 20 is comprised of electro-conductive neoprene rubber cement with carbon black dispersed uniformly throughout. It is thinned with a suitable solvent, such as toluene, at a ratio of approximately four to one, or as required to obtain satisfactory spray patterns. Successive coats are then sprayed upon the blade to obtain the desired thickness. The minimum limit of thickness is presently thought to be approximately .001 of an inch, the maximum limit of thickness approximately .004 of an inch, andtheoptimum thicknessfrom 09210- 2 of'aninch. An ir yingtimecfapproxir mately ten hours followed by baking for a period of from three to five hours at a temperature ranging from 150 to 190 F. will serve to insure evaporation of all solvents and to partially cure the neoprene rubber. While baking may be accomplished by any of a number of well known means, it has been found that infra-red lamps provide adequate heat without inhibiting ventilation and are, therefore, well suited for the purposes of this invention.

This final layer -oforganic material has as its primary function'the prevention of crack propagation; from the nickel plate 22 which-- is, of a relatively brittle nature to the base blade 10. In this connection, itiscarefully selected so as to havev the desired resiliency and the thickness limits are somewhat critical. If, on one hand, the layer 20 is of insufficient thickness, it will be incapable of accomplishing its function of prevention of crack propagation. On the other hand, if the layer is too thick, the nickel plate may tend to shift under certain anticipated conditions and bringshearstress into the adhesive system as a material consideration. Since thecharacteristics of the-layer 20 in thisrespect are, of course, predicated upon the inherent resiliency of the material as well as the thickness, it is essential also that the material selected have the desired resiliency. The neoprene rubber cement utilized in this invention is found to be particularly well suited to this use.

After baking, the blade is permitted to cool and is rinsed with water, then the conductive neoprene rubber cement surface is rubbed lightly with an abrasive paper to present a suitably smooth surface for nickel plating.

The blade is thendisposed in a conventional electrolytic nickel plating bath with the base blade connected as the cathode. Since all of the aforementioned blade covering layers are conductive throughout their respective thicknes'ses and. since the aluminum base blade serves as an efiicient cathode by virtue of its low resistance to current flow, deposition of the nickel commences over the entire blade surfacesimultaneously and the plating process isaccomplished in its ent-irety'muchmore quickly than has heretofore been the case. As indicated above, previously used plating processes of this type depended upon a relatively thin layer of conductive material disposed on the outermost organic layer as the cathode in the nickel plat ing bath. With the blade of this invention, the resistance to current flow in the base blade 10 and outwardly therefrom to the surface of the outermost organic layer 20 is of course much lower than in the case where the current must flow over the entire blade area within a thin conductive coating. Thus, itwill be seen that a distinctive feature of this invention is the utilization of the base blade 10' as the cathode in the nickel plating bath wherein the final nickel plate layer 22 is applied.

As a result of the rapid deposition of the nickel layer 22 over the entireblade surface, there is insufficient time for the plating bath to become contaminated as a result of chemical action of the bath with the organic materials. As a consequence, it becomes unnecessary to remove-the blade from the bath, substitute a clean bath and continue with the operation as was heretoforethe practice. The nickel plating process is thus accomplished much more rapidly and, furthermore, due tothe absence of contamination in the electrolytic bath, an extremely pure nickel plate is achieved. 7

As a further result of the rapid plating achieved over the entire blade surface, there is considerably less danger of the plating-bath components permeating the organic materials and causing corrosion of the base blade.

It will be quite apparent that the nickel plated aluminum aeronautical propellerblade provided in accordance with the aforedescribed specific process will comprise an aluminum air-foil body surrounded by layers of corrosion resistant zinc 1'2 and 14, a body of electroconductive-organic material comprising-the layers 16, 18 and 20 and an outermost layer ofnickel 22* or some othersuitably hard and wear-resistant metal. More specifically, the electro-conductive organie materials comprise, in inner to outer order, a layer of an electro-conductive synthetic rubber resin adhesive 16, a layer of electro-conductive resin modified neoprene cement 18 and a final layer of electro-conductive neoprene rubber cement 20.

As indicated above, an aeronautical propeller blade protectively plated in accordance with this invention has superior characteristics with respect to lightning strikes thereupon. In the case of aluminum blades plated in accordance with nickel plating processes known heretofore, wherein the finished article comprised succeeding layers of electro-conductive, dielectric and electro-conductive materials, reaction of the plated blade to a lightning strike is similar to that which might be expected of an electrical condenser. That is, an electrical charge could be expected to build up on the outer surface of the plated blade and, upon reaching a given potential, arcing would be expected to occur across the dielectric to the second conductor, the base aluminum blade. As a result of this action, it has been found that serious damage has been done to the structural integrity of the base blade. Furthermore, this damage has been of a particularly dangerous type due to the fact that, in many cases, it has not been apparent on the outer nickel plate surface.

In the case of the plated aeronautical propeller blade of this invention wherein all of the materials atfixed to the surface of the base aluminum blade are electrically conductive in their entirety, the reaction to a lightning strike is of a much more desirable nature. The electrical charge comprising the lightning bolt may be expected to pass through the aforesaid electro-conductive materials without first building up to an excessive potential, travel down the length of the propeller blade and into the airplane structure wherein it may either be dissipated or are across an air gap into the wing, tail section or other protruding portions of the airplane. The damage to the base aluminum blade, which results from a lightning strike in the case of propeller blades plated in accordance with processes known heretofore, would not be expected to occur due to the absence of the build up of an excessive electrical charge at the nickel plate surface and subsequent arcing across the dielectric organic materials to the base aluminum blade.

While the electro-conductive organic materials utilized have heretofore been referred to specifically as synthetic rubber resin adhesives, resin modified neoprene cement and neoprene rubber cement, it is to be understood that other adhesives having similar characteristics may be employed provided that an electro-conductive substance is dispersed uniformly throughout the same. In this connection, it is to be understood that wherever the terms synthetic rubber and/ or neoprene rubber are used, it is contemplated that natural rubber products may be utilized interchangeably therewith.

It should further be understood that modification may be undertaken within the scope of the invention by providing the electro-conductive organic materials beneath the nickel plate in a dilferent manner. Accordingly, it is not my intent to limit the invention to the particular process and blade described otherwise than indicated by the claims which follow.

The invention claimed is:

1. An aeronautical propeller blade which is electrically conductive throughout and which comprises an aluminum airfoil body plated with a hard wear resistant metal and a body of resilient organic material interposed between the aluminum body and the hard wear resistant metal plate, the said body of resilient organic material being electrically conductive throughout.

2. An aeronautical propeller blade which is electrically conductive throughout and which comprises an aluminum airfoil body plated with a hard wear resistant metal and a layer of corrosion resistant material and a body of resilient organic material interposed between the aluminum body and the hard wear resistant metal plate in innerto-outer order, said layer of corrosion resistant material and body of resilient organic material each being electrically conductive throughout.

3. An aeronautical propeller blade which is electrically conductive throughout and which comprises a nickel plated aluminum airfoil body having a body of rubberlike material interposed between the aluminum body and the nickel plate, the said body of rubber-like material being electrically conductive throughout and including a plurality of layers of adhesives which layers comprise in inner-to-outer order a layer of a synthetic rubber resin adhesive particularly suited for bonding with aluminum, a layer of a resin modified synthetic rubber cement particularly suited for bonding with synthetic rubber resin adhesives and with synthetic rubber adhesives, and a layer of a synthetic rubber adhesive.

4. An aeronautical propeller blade which is electrically conductive throughout and which comprises a nickel plated aluminum airfoil body and a layer of zinc and a body of rubber-like material interposed between the aluminum body and the nickel plate in inner-to-outer order, the said body of rubber-like material being electrically conductive throughout and including a plurality of layers of adhesives which layers comprise, in inner-to-outer order, a layer of synthetic rubber resin adhesive particularly suited for bonding with zinc, a layer of a resin modified synthetic rubber cement particularly suited for bonding with synthetic rubber resin adhesives and with synthetic rubber adhesives, and a layer of a synthetic rubber adhesive.

5. An aluminum aeronautical propeller blade which is electrically conductive throughout and which comprises a layer of zinc, an intermediate body of rubber-like material and an outer layer of nickel, the said body of rubber-like material being electrically conductive throughout by virtue of the dispersion of carbon black therethrough and including a plurality of layers of adhesives which layers comprise, in inner-to-outer order, a layer of a synthetic rubber resin adhesive particularly suited for bonding with Zinc ,no less than .0001 inch and no more than .0005 inch thick, a layer of a resin modified synthetic rubber adhesive particularly suited for bonding with synthetic rubber resin adhesives and with synthetic rubber adhesives no less than .0002 inch and no more than .001 inch thick, and a layer of synthetic rubber adhesive no less than .001 inch and no more than .004 inch thick.

References Cited in the file of this patent UNITED STATES PATENTS 741,413 Reed Oct. 13, 1903 1,589,324 Beal June 15, 1926 1,627,900 Hewitson May 10, 1927 2,217,719 Williams Oct. 15, 1940 2,637,404 Bart May 5, 1953 2,732,020 Scholl Jan. 24, 1956 2,739,932 Forestek Mar. 27, 1956 2,776,253 Scholl Jan. 1, 1957 2,776,254 Bart Jan. 1, 1957 FOREIGN PATENTS 472,570 Italy June 25, 1952 

1. AN AERONAUTRICAL PROPELLER BLADE WHICH IS ELECTRICALLY CONDUCTIVE THROUGHOUT AND WHICH COMPRISES AN ALUMINUM AIRFOIL BODY PLATED WITH A HARD WEAR RESISTANT METAL AND A BODY OF RESILIENT ORGANIC MATERIAL INTERPOSED BETWEEN THE ALUMINUM BODY AND THE HARD WEAR RESISTANT METAL PLATE, THE SAID BODY OF RESILIENT ORGANIC MATERIAL BEING ELECTRICALLY CONDUCTIVE THROUGHOUT. 